2.4 Naming Standard Input

Often, you may wish to read standard input together with other files.
For example, you may wish to read one file, read standard input coming
from a pipe, and then read another file.

The way to name the standard input, with all versions of awk,
is to use a single, standalone minus sign or dash, ‘-’. For example:

some_command | awk -f myprog.awk file1 - file2

Here, awk first reads file1, then it reads
the output of some_command, and finally it reads
file2.

You may also use "-" to name standard input when reading
files with getline (see Getline/File).

In addition, gawk allows you to specify the special
file name /dev/stdin, both on the command line and
with getline.
Some other versions of awk also support this, but it
is not standard.
(Some operating systems provide a /dev/stdin file
in the file system, however, gawk always processes
this file name itself.)